Trajectories of cholinergic pathways within the cerebral hemispheres of the human brain

All sectors of the human cerebral cortex receive dense cholinergic input. T he origin of this projection is located in the Ch4 cell group of the nucleu s basalis of Meynert, However, very little is known about the location of t he pathways which link the cholinergic neurons of the nucleus basalis to th e human cerebral cortex. This question was addressed in whole-hemisphere se ctions processed for the visualization of multiple cholinergic markers. Two highly organized and discrete bundles of cholinergic fibres extended from the nucleus basalis to the cerebral cortex and amygdala and were designated as the medial and lateral cholinergic pathways. These bundles contained ac etylcholinesterase, choline acetyltransferase and nerve growth factor recep tors, confirming their cholinergic nature and origin within the basal foreb rain, The medial pathway joined the white matter of the gyrus rectus, curve d around the rostrum of the corpus callosum to enter the cingulum and merge d with fibres of the lateral pathway within the occipital lobe, It supplied the parolfactory, cingulate, pericingulate and retrosplenial cortices, The lateral pathway was subdivided into a capsular division travelling in the white matter of the external capsule and uncinate fasciculus and a perisylv ian division travelling within the claustrum, Branches of the perisylvian d ivision supplied the frontoparietal operculum, insula and superior temporal gyrus, Branches of the capsular division innervated the remaining parts of the frontal, parietal and temporal neocortex, Representation of these chol inergic pathways within a 3D MRI volume helped to identify white matter les ion sites that could interfere with the corticopetal flow of cholinergic pa thways.